To add to what John has said, somtime they glue two elements together basicly making it one solid element. This is the glue joint that John speaks of. Even some high end lens can have this issue and I have seen it on several Mamiya lens. Have yet to see it cause a problem however. I had a 80mm for a Mamiya C330 that did this,and the 90mm C lens on my RB67 also has an element seperating. Still my most used lens.
Originally Posted by John Koehrer
Like John said, if you have choice get one with out it, but if the only one you can find do show signs of seperation, just point it out to the seller and ask for price break. Explain how you will have to have that repaired before useing it!!
Unless its very advanced, I don't think it will make a difference you can see in your prints/scans.
The big problem now is to show you what it looks like.